A mumps outbreak at the University of Missouri continues to grow with 31 confirmed cases.

The university also said Wednesday that there are another 27 probable cases of people who have been in close contact with someone with confirmed mumps showing symptoms for at least two days. The university said it's working with health officials to control the outbreak.

Mumps is a viral infection that causes swelling in the salivary glands and cheeks. Anyone with symptoms is asked to stay at home.

Mumps have been on the rise nationally this year. The Centers for Disease Control and Prevention said 2,345 mumps cases had been reported as of last month. That's more than twice as many as in all of 2015.

Other universities also have reported cases this year, including Harvard.